When ball may be changed

You may play any conforming ball when starting a hole from the teeing area and may change balls between two holes. You must hole out with the same ball you played from the teeing area, except when:

That ball is lost or comes to rest out of bounds, or
You substitute another ball (whether or not you are allowed to do so).

For example while playing a hole, you are allowed to use either the original ball or another ball:

When taking relief by dropping or placing, or
When playing again from where a previous stroke was made.

When replacing a ball on a spot you must use the original ball, with certain exceptions contained in Rule 14.2a. If you make a stroke at an incorrectly substituted ball you get one penalty stroke and you must then play out the hole with the incorrectly substituted ball.

Related Rule - 6.3